IR-reflecting compositions

Abstract

A composition comprising multistage polymeric particles having an average particle diameter from 0.5 to 15 μm and a Vicker's scale hardness from 100 to 700 Kgf/mm 2 ; and a film-forming polymer having T g no greater than 80° C. The refractive index difference measured from 400 nm to 800 nm between the polymeric particles and the film-forming polymer is no greater than 0.02 and the average refractive index difference measured from 800 nm to 2500 nm between the polymeric particles and the film-forming polymer is at least 0.04.

The invention claimed is: 
     
       1. A composition comprising polymeric particles having: (a) an average particle diameter from 0.5 to 15 μm; and (b) a Vicker's scale hardness from 100 to 700 Kgf/mm 2 ; and a film-forming polymer having T g  no greater than 80° C.; wherein an average refractive index difference measured from 400 nm to 800 nm between the polymeric particles and the film-forming polymer is no greater than 0.02 and an average refractive index difference measured from 800 nm to 2500 nm between the polymeric particles and the film-forming polymer is at least 0.04. 
     
     
       2. The composition of  claim 1  in which the average refractive index difference measured from 400 nm to 800 nm between the polymeric particles and the film-forming polymer is no greater than 0.01 and the average refractive index difference measured from 800 nm to 2500 nm between the polymeric particles and the film-forming polymer is at least 0.08. 
     
     
       3. The composition of  claim 2  in which the average particle diameter is from 1.5 to 10 μm. 
     
     
       4. The composition of  claim 3  in which the polymeric particles have a refractive index from 1.57 to 1.63. 
     
     
       5. The composition of  claim 4  in which the polymeric particles are: (a) particles having T g  from 75 to 150° C.; (b) particles having at least 0.5% polymerized residues of crosslinkers; or (c) a combination thereof. 
     
     
       6. The composition of  claim 5  in which the polymeric particles have T g  from 75 to 150° C. 
     
     
       7. The composition of  claim 6  in which a weight ratio of film-forming polymer to polymeric particles is from 2.2:1 to 3:1. 
     
     
       8. The composition of  claim 7  in which the composition is an aqueous emulsion of the polymeric particles. 
     
     
       9. The composition of  claim 8  in which the polymeric particles have a radial refractive index gradient wherein the particles have a refractive index at the center from 1.45 to 1.55 and a refractive index at the surface from 1.58 to 1.62. 
     
     
       10. The composition of  claim 9  in which the composition is substantially free of pigments or solid inorganic particles.